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Flexible Graphene/Carbon Nanotube Electrochemical Double-Layer Capacitors with Ultrahigh Areal Performance

The fabrication of electrochemical double-layer capacitors (EDLCs) with high areal capacitance relies on the use of elevated mass loadings of highly porous active materials. Herein, we demonstrate a high-throughput manufacturing of graphene/nanotubes hybrid EDLCs. Wet-jet milling (WJM) method is exploited to exfoliate the graphite into single/few-layer graphene flakes (WJM-G) in industrial volume (production rate ~0.5 kg/day). Commercial single/double walled carbon nanotubes (SDWCNTs) are mixed with graphene flakes in order to act as spacers between the graphene flakes during their film formation. The latter is obtained by one-step vacuum filtration, resulting in self-standing, metal- and binder-free flexible EDLC electrodes with high active material mass loadings up to 30 mg cm-2. The corresponding symmetric WJM-G/SDWCNTs EDLCs exhibit electrode energy densities of 539 uWh cm-2 at 1.3 mW cm-2 and operating power densities up to 532 mW cm-2 (outperforming most of the EDLC technologies). The EDCLs show excellent cycling stability and outstanding flexibility even under highly folded states (up to 180 degrees). The combination of industrial-like production of active materials, simplified manufacturing of EDLC electrodes, and ultrahigh areal performance of the as-produced EDLCs are promising for novel advanced EDLC designs.